In the control of compression-ignition internal combustion, or diesel engines, the conventional practice utilizes electronic control units having volatile and nonvolatile memory, input and output driver circuitry, and a processor capable of executing a stored instruction set, to control the various functions of the engine and its associated systems. A particular electronic control unit communicates with a plethora of sensors, actuators, and other electronic control units necessary to control various functions which may include fuel delivery, cooling fan control, engine speed governing and overspeed protection, engine braking, torque control, vehicle speed control, or myriad others.
Traditionally, complex systems and subsystems which perform critical functions required separate control units which could promptly respond to dynamic vehicle situations and initiate appropriate actions. For example a vehicle may have employed a brake controller, a cruise control module, a cooling fan controller, an engine controller, and a transmission controller such that each vehicle system or subsystem had its own stand-alone controller. These controllers were either electronic control units or electronic circuits which may have had little or no communication among themselves or with a master controller. Thus the vehicle operated by necessity as a distributed control system which often made it difficult to optimize overall vehicle performance, by coordinating control of the various systems and subsystems.
As control systems became more sophisticated, the various distributed controllers were connected to communicate status information and coordinate actions. However, inter-controller communication delays were often unacceptable for critical control tasks, thus requiring independent processors or circuitry for those tasks. This expanded the overall capabilities of the control system and was often necessary to meet increasing consumer demands as well as more stringent emission control standards. More recently, noise control standards have been implemented which are of special concern to diesel engine applications.
To meet these stricter standards, it has been necessary to expand the capabilities of the engine control system to more accurately control the engine operation. The complexity of the resulting control systems has often resulted in difficulty in manufacturing, assembling, and servicing them. Manufacturers have attempted to decrease part proliferation, while increasing the accuracy of control, by combining increasingly more control functions into one controller.
Advancements in microprocessor technology have facilitated the evolution of engine control systems. These systems began by implementing relatively simple control functions with mechanical apparatus, and progressed to more involved control schemes with dedicated controllers, before having matured as complex control strategies realized by a comprehensive engine controller. Many engine control systems found in the prior art address only a single subsystem control strategy and fail to capitalize on the advantages afforded by these microprocessor advancements. For example, U.S. Pat. No. 4,782,803 issued to Kikuchi discloses a stand-alone system and associated method of fuel injection control for compression-ignition internal combustion engines. However, there are no provisions for integrating the control of fuel delivery with other functions to harmonize control of the engine and vehicle subsystems. This is necessary to optimize performance in areas such as fuel economy, driveability, noise, and emissions.
Traditionally, emission control standards could be satisfied using control strategies which responded only to changes in local operating conditions such as engine load and temperature. A comprehensive integrated control strategy was unnecessary and often difficult or economically unfeasible to implement. However, more exacting emissions standards would require emissions to respond to the global operating environment which varies much more slowly than the local conditions. The global operating environment may be indicated by trends in the local operating conditions. For example, the frequency of engine speed changes and transmission gear-state changes, which are local operating conditions, could indicate whether the vehicle is in a city environment or a rural highway environment. In a city environment, it is desirable to reduce nitrogen oxide (NO.sub.x) emissions, which contribute to smog, but this is at the expense of increasing carbon dioxide (CO.sub.2) emissions. Whereas the converse is true in a rural environment, where it is desirable to reduce CO.sub.2 emissions at the expense of increasing NO.sub.x emissions.
Another difficulty encountered by traditional, distributed engine control systems is the inability to protect the engine from system failures which may be manifested in excessive temperatures or inadequate pressures. Traditionally, major system failures would result in either an immediate engine shutdown, or a simple diagnostic code which would alert the operator of the malfunction.
Another feature traditionally found in engine controllers, and especially in diesel engine controllers, is the ability to automatically control vehicle speed, generically referred to as cruise control. Most conventional systems utilize some form of engine fuel supply regulation to maintain a desired vehicle speed. However, heavy vehicles, such as loaded semi-trucks, often exceed the selected desired speed on long grades, since, even though little or no fuel is supplied to the engine, gravitational pull continues to accelerate the vehicle down an incline and requires manual braking to limit vehicle speed. Thus, these vehicle speed control systems have a limited region of control since they are not integrated with other vehicle systems.
A diagnostic or monitoring feature traditionally available in engine controllers, especially in commercial vehicle applications, is the ability to oversee vehicle operating speeds. For example, excessive road speeds may be logged by the controller for later review by the vehicle owner to encourage safe operation and discourage excessive stoppage by the vehicle operator. However, this often results in less than optimal vehicle performance since many operators may maintain a speed lower than necessary to avoid having an excessive speed code logged against them. For example, if the owner sets the excessive speed code at 58 m.p.h. then the operator may attempt to maintain a speed of only 53 m.p.h. to avoid crossing that threshold. Furthermore, the operator cannot take advantage of the momentum gained when descending grades if the vehicle speed would exceed the established limit. Both of these scenarios result in decreased overall fuel economy and unnecessary braking.
The desire to provide application specific vehicles at a competitive price has led to the availability of a number of customer options which may include some of the systems already noted such as vehicle speed control, engine speed control, or engine torque control. This in turn has lead to a large number of possible subsystem combinations, thus increasing the costs associated with manufacturing and assembly as well as the cost of field service due to the large number of spare components which must be manufactured and stored.
It is desirable to have an electronic control unit capable of integrating the control of various engine functions and associated vehicle systems thus eliminating inter-controller communication delays and harmonizing engine control with other vehicle subsystems. An additional benefit accrues from replacing independent stand-alone controllers with a comprehensive controller, thus reducing part proliferation in the manufacturing, assembly, and service environments, leading to an associated reduction in the cost of these functions.
It is also desirable in optimizing overall vehicle performance, to have an electronic control unit which coordinates control of the combustion process with other systems and subsystems to adapt to changing operating conditions for the purpose of minimizing noise and emissions while improving qualitative engine attributes such as idle quality. For example, noise is most prevalent in diesel engines at idle or under low load conditions. It is therefore desirable to modify the combustion process in those situations to reduce ignition delay which results in a reduction of noise. Furthermore, it is desirable to carefully control the combustion process to balance the power output of individual cylinders to improve the idle quality while also reducing noise.
It is further desirable to modify the combustion process to adapt to changing global conditions, since this optimizes emissions at all times. This is a distinct advantage over traditional controller systems which attempt to average emissions over all operating conditions, which leads to less than optimal performance in vehicles which are exclusively used in city environments or in rural environments.
It is also desirable to have a single electronic control unit capable of controlling various subsystem configurations which may contain components produced by different manufacturers. This allows further reduction in part proliferation and accrues the benefits already noted. For example, the recently proposed Truck Maintenance Council (TMC) standard requires that a cooling fan control module be capable of controlling any one of four fan configurations including a single one-speed fan, dual one-speed fans, a single two-speed fan, or a single variable speed fan. This simplifies maintenance by reducing the burden of matching appropriate component parts with compatible controllers.
It is also desirable to implement vehicle speed control with an electronic control unit which integrates control of fuel delivery with engine braking and engine accessory load. This expands the authority of the vehicle speed control by providing ancillary speed limiting capabilities in addition to restricting fuel delivery to the engine.
In enhancing vehicle performance, and especially in optimizing-fuel economy, it is desirable to monitor the vehicle speed to alert the operator of an impending excessive speed violation in time for an appropriate action prior to the violation actually being logged. Furthermore, it is desirable to allow the vehicle speed to exceed the selected maximum speed without logging a violation under certain conditions, such as when the vehicle is descending a grade or coasting after descending a grade.
It is also desirable to protect the engine from system malfunctions while allowing the operator to safely bring the vehicle to a stop. For example, if oil pressure is insufficient for safe engine operation, it is desirable to steadily decrease the output torque of the engine so that the vehicle can be maneuvered to an acceptable location and an orderly engine shut-down performed to avoid catastrophic engine failure while not endangering the operator.
It is further desirable to protect other vehicle systems and components, such as the transmission, by limiting the engine output torque and output speed under certain operating conditions. One advantage of controlling engine output torque is utilizing a single engine family (engines with similar output torque) with a plurality of transmission families, since the engine torque can be limited to the rated torque of the transmission. Similarly, engine torque can be limited to protect drive line components when mechanical torque multiplication is greatest, as when the transmission is in its lowest gear, but allowing full engine torque in higher gears, thus reducing the necessity of downshifting, such as when climbing hills at highway speeds.
In controlling systems or functions, such as engine output torque or output speed, it is desirable to utilize the largest system gain which results in an acceptable overshoot, to decrease the response time of the control system while increasing its accuracy.